Methods for improving the resistance to hydrolysis in polyurethane (pu)-based systems

ABSTRACT

The invention relates to novel processes for improving hydrolysis resistance in polyurethane (PU) based systems, preferably PU adhesives, PU casting resins, PU elastomers or PU foams.

The invention relates to novel processes for improving hydrolysisresistance in polyurethane (PU) based systems, preferably PU adhesives,PU casting resins, PU elastomers or PU foams.

Polyurethanes are formed, almost quantitatively, by polyadditionreaction of polyisocyanates with polyhydric alcohols, i.e. polyols.Linking ensues by the reaction of an isocyanate group (—N—C═O) of onemolecule with a hydroxyl group (—OH) of another molecule to form aurethane group (—NH—CO—O—).

The course of the reaction between the diisocyanate and the polyoldepends on the molar ratio between the components. Intermediate productshaving a desirable average molecular weight and desirable end groups maywell be formed. These intermediate products can then be chain extendedlater by reaction with a diol or diamine to form the desiredpolyurethane or polyurethane-polyurea hybrid. These intermediateproducts are generally known as prepolymers.

Suitable polyols for forming prepolymers include not only diols but alsopolyalkylene glycol ethers, polyether esters or polyesters havingterminal hydroxyl groups (polyester polyols).

Polyester polyols are preferably used to form polyurethanes designed tohave high mechanical or dynamical fatigue resistance.

The polyether esters or polyesters with terminal hydroxyl groups thatare formed by polycondensation of simple diols and carboxylic acidsstill contain free carboxylic acids. These catalyse the reaction betweenthe ester groups in the polymer and water, and this leads to a low levelof hydrolysis resistance.

Currently commercially available carbodiimides, as described in EP-A0799843, are too sluggish for rapid acid removal within the time inwhich the prepolymers are prepared and made available for furtherprocessing to form the cured polymer, or insufficiently soluble to bepractical and economical.

The problem addressed by the present invention was therefore that ofproviding processes for improving the hydrolysis resistance ofpolyurethane (PU) based systems, that are useful in particular for theproduction of PU adhesives, PU casting resins, PU elastomers or PUfoams, while eschewing materials that are costly and inconvenient toproduce.

The problem was surprisingly solved by the process of the presentinvention in which specified carbodiimides are added to the polyol.

The present invention accordingly provides a process for improvinghydrolysis resistance in polyurethane (PU) based systems, in which

-   -   at least one carbodiimide of formula (I)

where m is 0-10,R¹, R³ and R⁵ are each independently H or methyl,R² and R⁴ are each independently H, methyl, NH—C(O)—OR¹⁰, whereR¹⁰ is C₁-C₄-alkyl or—(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹,where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl,and R⁶, R⁷, R⁸ and R⁹ are each independently H or methyl, andat least one diisocyanate and optionally a diamine and/or a diol arestirred into

-   -   at least one polyol selected from the group of polyester polyols        and/or polyetherester polyols at temperatures in the range from        0° C. to +130° C., preferably +10° C. to +60° C., more        preferably +15° C. to +30° C.

In a preferred embodiment of the invention, m is 0 and

R¹, R³ and R⁵ are each independently H or methyl,R² and R⁴ are each independently H, methyl or —NH—C(O)—OR¹⁰, where R¹⁰is C₁-C₄-alkyl or —(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹,where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl,preferably R¹, R³, R⁴ and R⁵ are each H or methyl, more preferably R¹,R³ and R⁵ are each methyl and R⁴ is H,R² is —NH—C(O)—OR¹⁰, where R¹⁰ is —C₁-C₄-alkyl or—(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹,where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl.

It is very particularly preferable in the case of m=0 when R¹ is methyland R², R³, R⁴ and R⁵ are each H.

It is likewise very particularly preferable in the case of m=0 when

R³ or R⁵ is methyl or H,R² is —NH—C(O)—OR¹⁰, where R¹⁰ is —C₁-C₄-alkyl or—(CH₂)_(h)—(O—(CH₂)_(k)—O)_(g)—R¹¹,where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyland R¹ and R⁴ are each H.

In a further likewise preferred embodiment of the invention, m is >0,more preferably m is 1, with R¹, R³ and R⁵ each independently being H ormethyl, and

R² and R⁴ are each H, methyl or —NH—C(O)—OR¹⁰, where R¹⁰ is C₁-C₄-alkylor —(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹,where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl,provided one or more of R⁶, R⁷, R⁸ and R⁹ are each independently H ormethyl,preferably R¹, R³, R⁴ and R⁵ are each H or methyl, more preferably R¹,R³ and R⁵ are each methyl and R⁴ is H,R² and R⁴ are each H, methyl or —NH—C(O)—OR¹⁰, where R¹⁰ is C₁-C₄-alkylor —(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹,where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl,provided one or more of R⁶, R⁷, R⁸ and R⁹ are each independently H ormethyl,

It is further preferable when R¹, R³, R⁴, R⁵ are each H or methyl, morepreferably methyl,

R² is —NH—C(O)—OR¹⁰, where R¹⁰ is —C₁-C₄-alkyl or—(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹,where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl,R⁶, R⁷, R⁸ and R⁹ are each independently H or methyl and more preferablyat least one of R⁶, R⁷ and R⁹ is methyl.

It is likewise highly preferable in the case of m=1 when

R³ or R⁵ is methyl or H,R² is —NH—C(O)—OR¹⁰, where R¹⁰ is —C₁-C₄-alkyl or—(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹,where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl,and R¹ and R⁴ are each H andR⁶, R⁷, R⁸ and R⁹ are each independently H or methyl, preferably atleast one of R⁶, R⁷ and R⁹ is methyl.

In a preferred embodiment of the invention, at least one of R⁷ and R⁹ ismethyl.

The compounds of formula (I) are commercially available substances inthat they are available from Rhein Chemie Rheinau GmbH, for example,under the trade names Stabaxol® and Hycasyl® for example.

Preference is likewise given to mixtures of two or more carbodiimides,at least one of which corresponds to formula (I). In the case of amixture, mean m can also be a fractional number.

Polyols for the purposes of the invention are selected from the group ofpolyester polyols and/or polyetherester polyols.

Polyester polyols for the purposes of the invention are compounds with amolecular weight in g/mol of preferably up to 2000, more preferably inthe range from 500 to 2000 and yet more preferably in the range from 500to 1000.

The term polyesterpolyols is to be understood as meaning for thepurposes of the present invention not only compounds having two or threehydroxyl groups per molecule but also compounds having more than threehydroxyl groups per molecule.

Polyester polyols are preferred polyols. It is advantageous for thepolyester polyols and/or polyetherester polyols to have an OH number ofup to 200, preferably between 20 and 150 and more preferably between 50and 115.

Particularly suitable polyester polyols are reaction products of variousdiols with aromatic or aliphatic dicarboxylic acids and/or polymers oflactones.

Preference here is given to aromatic dicarboxylic acids useful forforming suitable polyester polyols. Particular preference is given hereto terephthalic acid, isophthalic acid, phthalic acid, phthalicanhydride and also substituted dicarboxylic acid compounds having abenzene ring.

Useful aliphatic dicarboxylic acids are preferably those aliphaticdicarboxylic acids useful for forming suitable polyester polyols, morepreferably sebacic acid, adipic acid and glutaric acid.

Preferred polymers of lactones are useful for forming suitable polyesterpolyols, more preferably polycaprolactone.

The dicarboxylic acids and the polymers of lactones are commerciallyavailable substances.

Particular preference is also given to those diols useful for formingsuitable polyester polyols, most preferably ethylene glycol, butanediol,neopentyl glycol, hexanediol, propylene glycol, dipropylene glycol,diethylene glycol and cyclohexanedimethanol.

In a further preferred embodiment of the invention, at least onepolyetherester polyol is used.

Preference for this is given to the reaction products of variousaforementioned polyols with aromatic or aliphatic dicarboxylic acidsand/or polymers of lactones (e.g. polycaprolactone).

The polyester polyols and/or polyetherester polyols used for thepurposes of the inventions are commercially available compounds in thatthey are available from Bayer MaterialScience AG under the trade name ofBaycoll® or Desmophen®.

Aromatic and aliphatic diisocyanates are preferred. Tolylene2,4-diisocyanate, tolylene 2,6-diisocyanate, phenylene diisocyanate,4,4-diphenylmethane diisocyanate, methylene bis(4-phenyl isocyanate),naphthalene 1,5-diisocyanate, tetramethylene 1,4-diisocyanate and/orhexamethylene 1,6-diisocyanate are particularly preferred and tolylene2,4-diisocyanate and tolylene 2,6-diisocyanate are very particularlypreferred.

The diisocyanates used for the purposes of the inventions arecommercially available compounds in that they are available from BayerMaterialScience AG under the trade name of Desmodur®.

In a further embodiment of the invention, the composition additionallycontains at least one diamine and/or diol.

Diamines, which are used for chain extension, are preferably2-methylpropyl 3,5-diamino-4-chlorobenzoate,bis(4,4′-amino-3-chlorophenyl)methane,3,5-dimethylthio-2,4-tolylenediamine,3,5-dimethylthio-2,4-tolylenediamine, 3,5-diethyl-2,4-tolylenediamine,3,5-diethyl-2,6-tolylenediamine,4,4′-methylenebis(3-chloro-2,6-diethylaniline) and 1,3-propanediolbis(4-aminobenzoate).

Preference for use as diols is given to butanediol, neopentyl glycol,hexanediol, propylene glycol, dipropylene glycol, diethylene glycoland/or cyclohexanedimethanol. 1,3-butanediol or 1,6-hexanediol areparticularly preferred.

The diamines or diols used for chain extension within the meaning of theinvention are commercially available compounds in that they areavailable from Rhein Chemie Rheinau GmbH under the trade name ofAddolink®.

Catalysts used are preferably dibutyltin dilaurates ortriethylenediamine in dipropylene glycol.

Catalysts used for the purposes of the inventions are commerciallyavailable compounds in that they are available from Rhein Chemie RheinauGmbH under the trade name of Addocat®.

The ratio of carbodiimide to polyol is preferably 0.1-5, more preferably1-3 parts by weight per 100 parts by weight of polyol.

The ratio of diisocyanate to polyol is preferably 20-50:100 parts byweight, more preferably 30:100 parts by weight.

In those cases where the composition contains at least one diamineand/or diol in addition to the polyester polyol and/or polyetheresterpolyol and the carbodiimide and also the diisocyanate, the amount ofdiamine and/or diol is 5-30 wt %, based on the composition.

In those cases where the composition contains at least one catalyst inaddition to the polyol and the carbodiimide and also the diisocyanate,the amount of catalyst is 0.01-1 wt %, based on the composition.

The polyurethane (PU) based systems obtained by this process haveincreased hydrolysis resistance.

The purview of the invention encompasses all the moiety definitions,indices, parameters and explications recited hereinabove and hereinbelowin general terms or in preferred ranges in combination with one another,including that is in any desired combination of the respective rangesand preferred ranges.

The examples which follow are offered by way of elucidation notlimitation of the invention.

WORKING EXAMPLES

The following substances were used in the examples which follow:

Baycoll® AV 2113: a branched polyester polyol having an OH number of 110mg KOH/g and an acid number of 0.83 mg KOH/g, from Bayer MaterialScienceAG.Stabaxol® I TC: a carbodiimide of formula (I) where m=0 and R¹═CH₃,R²═H, R³═H, R⁴═H and R⁵═H.CDI 1: carbodiimide of formula (I) where m=0 and R¹═CH₃, R⁴═H, R³═H,R²—NH—C(O)—OR and 5^(R)=H.Stabaxol® P 200: a polymeric aromatic carbodiimide based ontetramethylxylylene diisocyanate from Rhein Chemie Rheinau GmbH.Stabaxol® I: a monomeric carbodiimide based on 2,6-diisopropylphenylisocyanate from Rhein Chemie Rheinau GmbH.Desmodur® PU 0129: a 2,4/4,4 diphenylmethane diisocyanate isomermixture.Addolink® B: a 1,4-butanediol from Rhein Chemie Rheinau GmbH as diolcomponent.Addocat® 201: a dibutyltin dilaurate from Rhein Chemie Rheinau GmbH, ascatalyst.Carbodilite® HMV-8 CA: a polymeric aliphatic carbodiimide from NisshinboIndustries, INC.One portion of the formulation further contains a molecular sieve formoisture adsorption.Desmocoll® 140: a substantially linear hydroxyl polyurethane having ahydroxyl content <0.1 from Bayer MaterialScience AG.Baycoll® AS 2060: a lightly crosslinked polyester polyol having ahydroxyl number of 60±3 mg KOH/g and an acid number of ≦2.0 mg KOH/gfrom Bayer MaterialScience AG.Desmodur® RFE: a solution of tris(p-isocyanatophenyl)thiophosphate inethyl acetate having an NCO content of 7.2±0.2% as isocyanate curativefrom Bayer MaterialScience AG.

Example 1

The following mixtures were produced as follows:

Mixture A (comparator): 100 g of the room temperature liquid Baycoll® AV2113.Mixture B (for preparing mixture II of resent invention): 100 g of theroom temperature liquid Baycoll® AV 2113 were admixed with 0.6 g of thecarbodiimide of formula (I) where m=0 and R¹═CH₃, R²═H, R³═H, R⁴═H andR⁵═H (Stabaxal® I TC) and stored at 30° C. for 24 h.Mixture C (comparator): 100 g of the room temperature liquid Baycoll® AV2113 were admixed with 0.6 g of Stabaxol® I and stored at 30° C. for 24h.Mixture D (comparator): 100 g of the room temperature liquid Baycoll® AV2113 were admixed with 0.6 g of Stabaxol® P 200 and stored at 30° C. for24 h.Mixture E (comparator): 100 g of the room temperature liquid Baycoll® AV2113 were admixed with 0.6 g of Carbodilite® HMV-8 CA and stored at 30°C. for 24 h. The two substances cannot be mixed. So this mixture was notemployable for further tests.

The acid number of the mixtures was measured in accordance with DIN53402 after storage. The results are shown in table I:

TABLE 1 acid number mg KOH/g mixture A (comparator) 0.83 mixture B 0.30mixture C (comparator) 0.80 mixture D (comparator) 0.60

The particular composition of the elastomers obtained is apparent fromtable 2. All particulars are in parts by weight, unless otherwisestated.

TABLE 2 mixture A mixture C mixture D Addocat ® Addolink ® Desmodur ®(comparator) mixture B (comparator) (comparator) 201 B PU 0129 I (c) 1000.06 10 56 II(i) 100 0.06 10 56 III (c) 100 0.06 10 56 IV (c) 100 0.0610 56 c = comparative example; i = inventive example

All the mixtures additionally contained 5 parts by weight of molecularsieve for moisture absorption.

The mixtures were processed by the one-shot method, i.e. premixed withmolecular sieve, Addocat® 201 and Addolink® B and reacted with thediisocyanate (Desmodur® PU0129). The mixture which was initially liquidand reacted to form a solid elastomer after a few minutes was pouredinto a warm test mould at 30° C., demoulded after 1 h and conditioned at100° C. for 16 h.

Standard test specimens were die-cut out of the test sheets thusobtained for mixtures I to IV, after they had been stored at 22° C. for7 days.

The hydrolysis resistance of mixtures I to IV was determined as follows:

The die-cut standard test specimens were stored in water at atemperature of 80° C. for 4 days. The tensile strength of the testspecimens stored in water was measured after every 24 h.

Table 3 shows the percentage relative tensile strength starting at day 0with 100%.

TABLE 3 day 0 day 1 day 2 day 3 day 4 I (c) 100 80 70 60 50 II (i) 10090 90 90 80 III (c) 100 90 80 70 60 IV (c) 100 90 85 75 65 (c) =comparative example; (i) = inventive example

Example 2

The following mixtures were produced as follows:

Mixture A2 (comparator): 14 g of Desmocoll® 140 were dissolved in 75 gof ethyl acetate at 85° C. 7 g of Baycoll® AS 2060 were added duringcooling.Mixture B2 (comparator): 14 g of Desmocoll® 140 were dissolved in 75 gof ethyl acetate at 85° C. 7 g of Baycoll® AS 2060 were added duringcooling. 0.32 g of Stabaxol® I was dissolved in the cold mixture withstirring, followed by storage at room temperature for five days.Mixture C2 (to produce the inventive mixture): 14 g of Desmocoll® 140were dissolved in 75 g of ethyl acetate at 85° C. 7 g of Baycoll@AS 2060were added during cooling. 0.2 g of the carbodiimide of formula (I)where m=0 and R¹═CH₃, R²═H, R³═H, R⁴═H and R⁵═H (Stabaxol® I TC) wasdissolved in the cold mixture with stirring, followed by storage at roomtemperature for five days.Mixture D2 (to produce the inventive mixture): 14 g of Desmocoll® 140were dissolved in 75 g of ethyl acetate at 85° C. 7 g of Baycoll® AS2060 were added during cooling. 0.31 g of CDI I was dissolved in thecold mixture with stirring, followed by storage at room temperature forfive days.

TABLE 4 adhesive mixture mixture mixture mixture Desmodur ® number A2 B2C2 D2 RFE I (comparator) 96 g 4 g II(comparator) 96.32 g 4 g III 96.2 g4 g IV 96.31 g 4 g

Mixtures A2, B2, C2 and D2 were each admixed at room temperature with 4g of Desmodur® RFE isocyanate curative. Adhesives I, II, III and IV thusobtained were applied by hand with a wire-wound blade with 10 μm size toa commercially available. 23 μm thick, unpretreated DIN A4-sized PETsheet, although the topmost 50 mm of the sheet were not coated withadhesive owing to a protective strip to be removed later. The solvent ofthe adhesive (ethyl acetate) was subsequently flashed off at roomtemperature for five minutes. Then, a commercially available, 25 μmthick, unpretreated aluminium foil was laminated in place by hand. Thelaminate thus formed was cured at 50° C. under a moulding pressure of 10kg for one hour. Thereafter, the samples were stored under standardconditions for at least seven days, cut to size in accordance with ISO11339 and subjected to the hydrolysis resistance test. In this test, thestored samples were stored individually freely suspended in an autoclaveat 121° C. (250° F.) and 100% relative humidity for 30 min. Themeasurements were subsequently carried out at an extension rate of 100mm/min.

The results of the hydrolysis resistance tests are reported in table 5.

TABLE 5 adhesive 0 min storage 30 min storage number [N/100 mm] [N/100mm] I (comparator) 1.73 0.31 II (comparator) 1.74 0.29 III 1.53 1.33 IV1.39 1.34

Interpretation of Experimental Results:

The aromatic carbodiimides from the prior art exhibit no positive effectwith respect to the tensile shear strength compared to thecarbodiimide-free samples. In the examples according to the invention,by contrast, adhesives III and IV exhibit a markedly increasedhydrolysis resistance.

1. Process for improving the hydrolysis resistance of polyurethane (PU) based systems, the process comprising combining at least one carbodiimide of formula (I)

where m is O-10, R¹, R³ and R⁵ are each independently H or methyl, R² and R⁴ are each independently H, methyl, NH—C(O)—OR¹⁰, where R¹⁰ is C₁-C₄-alkyl, or —(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹, where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl, and R⁶, R⁷, R⁸ and R⁹ are each independently H or methyl, and at least one diisocyanate and optionally a diamine and/or a diol with at least one polyol selected from the group of polyester polyols and/or polyetherester polyols at temperatures in the range from 0° C. to +130° C.
 2. The process according to claim 1, wherein in the carbodiimide of formula (I), m is 0, R¹, R³ and R⁵ are each independently H or methyl, and R² and R⁴ are each independently H, methyl or —NH—C(O)—OR¹⁰, where R¹⁰ is C₁-C₄-alkyl or —(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹, where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl.
 3. The process according to claim 1, wherein in the carbodiimide of formula (I) m is >0, R¹, R³ and R⁵ are each independently H or methyl, R² and R⁴ are each independently H, methyl or —NH—C(O)—OR¹⁰, where R¹⁰ is C₁-C₄-alkyl or —(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹, where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl, and one or more of R⁶, R⁷, R⁸ and R⁹ are each independently H or methyl.
 4. The process according to claim 1, wherein the carbodiimides are mixtures of two or more carbodiimides, at least one of which corresponds to formula (I).
 5. The process according to claim 1, further comprising at least one catalyst.
 6. The process according to claim 1, further comprising using at least one diamine and/or diol.
 7. The process according to claim 1, further comprising adding, prior to the addition of the diisocyanate, at least one catalyst, and at least one diol, and optionally molecular sieves.
 8. The process according to claim 1, wherein the temperature is 10° C. to 60° C.
 9. The process according to claim 1, wherein the temperature is 15° C. to 30° C.
 10. The process according to claim 1, wherein in the carbodiimide of formula (I), m is 0, R¹, R³, R⁴ and R⁵ are each independently H or methyl, and R² is —NH—C(O)—OR¹⁰, where R¹⁰ is —C₁-C₄-alkyl or —(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹, where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl.
 11. The process according to claim 10, wherein R¹, R³ and R⁵ are each methyl and R⁴ is H.
 12. The process according to claim 1, wherein in the carbodiimide of formula (I) m is >0, R¹, R³, R⁴ and R⁵ are each H or methyl, R² is —NH—C(O)—OR¹⁰, where R¹¹ is —C₁-C₄-alkyl or —(CH₂)_(h)—O—[(CH₂)_(k)—O]_(g)—R¹¹, where h is 1-3, k is 1-3, g is 0-12 and R¹¹ is H or C₁-C₄-alkyl, and R⁶, R⁷, R⁸ and R⁹ are each independently H or methyl.
 13. The process according to claim 12, wherein R¹, R³ and R⁵ are each methyl, R⁴ is H, and at least one of R⁶, R⁷ and R⁹ is methyl.
 14. The process according to claim 7, wherein the at least one catalyst comprises dibutyltin dilaurate, and the at least one diol comprises 1,4-butanediol. 